This section provides background information related to the present disclosure which is not necessarily prior art.
Ultrasonic energy has been shown to be a useful tool in a wide variety of applications from very low power medical diagnostics through high intensity processes which change the state of materials. Joining of metals, specifically nonferrous metals used in electrical connections, is a particularly useful application of this technology. Commonly used techniques involving the fusion of metal through the application of heat by flame, hot tools, electric current or electric arc in combination with cleaning and fluxing agents and sometimes filler metals are able to join these materials but the characteristics of these processes and the materials to be joined are at odds with one another. Still, users have become accustomed to the problems associated with fusion welding to the point that the problems are considered “normal.”
Ultrasonic welding of nonferrous metals in electrical connections has been demonstrated to eliminate most, if not all, of these problems. In fact, ultrasonic welding of metals is rapidly becoming the process of choice by informed design and manufacturing engineers. The number of applications and reduced operating expenses have led to wide use of ultrasonic welding for wiring and interconnection applications.
Since the first ultrasonic welding machine for metals was developed and patented in 1960, there have been significant technological advances which now make the process a practical production tool. Early power supplies, employing vacuum tube technology, could not produce high power levels of ultrasonic energy and were inefficient and expensive. Early work was limited to research and development which showed the promise of the process and spurred further technical development. Today, ultrasonic energy in general is a well established tool of industry having applications in nondestructive testing, industrial ultrasonic cleaning, ultrasonic plastic joining and ultrasonic metal welding. Ultrasonic metal welding has much to offer the user including speed, efficiency, excellent weld quality, elimination of consumables, long tool life and the ability to be automated.
Generally, ultrasonic energy is mechanical vibratory energy which operates at frequencies beyond audible sound, or 18,000 Hz (18,000 Hz being the upper threshold of the normal human hearing range). Two basic frequencies are generally used; 20,000 Hz and 40,000 Hz, depending on the application. Selection is based upon the required power levels, the amplitude of vibration required and the size of the ultrasonic tool to be used. Frequency is important because it directly affects the power available and the tool size. It is easier to generate and control high power levels at the lower frequency. Also, ultrasonic tools are resonant members whose size is inversely proportional to their operating frequency. The generation of ultrasonic energy starts with conversion of conventional 50 or 60 Hz electrical power to 20,000 or 40,000 Hz electrical energy by a solid state power supply.